1. Field of the Invention
The present invention relates generally to three position hydraulic valves used in a wide variety of hydraulic applications. Hydraulic valves of this sort may be utilized, for example, to cause piston movement and thereby cause operation of hydraulic equipment. One example of such an application would be engine brakes. The present invention relates to an improved design for such hydraulic valves.
2. Brief Description of the Related Art
Prior art or traditional three position valves utilized two solenoid coils, with one solenoid associated with a pull pole piece and one solenoid associated with a push pole piece. A plunger was oriented between the two pole pieces with the neutral position for the plunger being mid-stroke between them. One or more return springs were provided for returning the plunger to the neutral mid-stroke position between the push and pull pole pieces.
When electrical current was applied to one of the solenoid coils, a magnetic force was created in the associated pole piece (either the push pole piece or the pull pole piece, respectively) which caused the magnetically responsive plunger to attempt to close the air gap between the magnetically operational pole piece and the plunger, causing the return spring or springs to compress. When the electrical current was removed from the solenoid, the magnetic force in the operational pole piece was removed, and the springs returned the plunger to the neutral mid-stroke position. The plunger movement was, in turn, mechanically transmitted to a spool type directional control valve, which, directed hydraulic fluid flow. On a traditional two coil, three position valve, the valve was required to move through a neutral position in order to transition from a first operating position (e.g., with the plunger magnetically attracted to push pole piece) to a second operating position (e.g., with the plunger magnetically attracted to pull pole piece).
The present invention, called a sequential stepped directional control valve, overcomes the problems associated with traditional three position valves. The present invention does not involve transitioning through a non-operational neutral position in order to change from a first stage operational position to a second stage operational position. Depending on the nature of the hydraulic application, such a transition through a neutral position, as described in more detail below, can be highly disadvantageous, dangerous, or even deadly. The present invention, moreover, is economical, and involves less parts that can lead to failure. Whereas traditional prior art three position hydraulic valves required two solenoids, and two pole pieces (a push and pull pole piece), the present invention requires only a single solenoid and a single pole piece, saving costs and decreasing complexity. By eliminating the extra traditional parts, the present invention can achieve a savings in size as well.